1. Field of the Invention
The embodiments of the invention generally relate to Serial Attached SCSI (SAS) standards, and, more particularly, to expanding the distance limitation in the SAS physical layer so that SAS storage protocol may be implemented between host systems and storage controllers in a storage area network.
2. Description of the Related Art
Storage area networks (SAN) allow for the exchange of data packets between physically separated host computer systems and storage devices. Specifically, data packets are transported via one or more switches to one or more storage controllers which control storage of the data on one or more storage devices. These host computer systems can include, but are not limited to, personal computers or servers (e.g., application servers or database servers). Storage devices can include, but are not limited to, tape drives, disk drives, or disk systems (e.g., redundant arrays of independent disks (RAID) systems). SANs generally use Fiber Channel (FC) protocol for host computer system to storage controller communication because the host computer system and storage controller are usually physically separated and FC protocol has a physical layer distance limitation of approximately 50 miles or less. Small Computer System Interface (SCSI) protocol or Serial Attached SCSI (SAS) is generally used for storage controller to storage device communication because each storage controller is typically located in the same physical location (e.g., in the same box) as multiple storage devices and SCSI and SAS protocols have a physical layer distance limitation of approximately 6 meters.
More specifically, Serial Attached Small Computer System Interface (SAS) standards typically provide commands, transport protocols (i.e., defined rules) and interfaces for physically connecting and exchanging information between different SAS devices (e.g., computers and peripheral devices, storage controllers and storage devices located in the same box, etc.). Additionally, SAS standards define the rules for physically connecting and exchanging information between Serial Advanced Technology Attachment (SATA) hosts and SATA devices (e.g., between computers and storage devices, such as hard disks or CD-ROMs), using the same serial interconnect. There are five layers to the SAS standards. These layers include the physical layer, the link layer, the port layer, the transport layer, and the application layer. In network environments in which the rules for exchanging data are defined by SAS standards, the physical layer is targeted for device level interconnects and the SAS physical layer is limited to a distance coverage of approximately 6 meters. Thus, SAS standards are generally considered suitable for storage controller to storage device communication, but not host computer system to storage controller communication. However, except for this distance limitation, SAS protocols could be suitably implemented instead of FC protocols in storage area networks (SAN) to define the rules for exchanging information between the host computer systems and storage controllers, especially for the low end.